Drying method



a- 1943. V R. A. BIE RWIRTH 2,325,652

DRYING METHOD I Filed Aug. 20, 1941 RED! 0 17 FREQUENCY OSCILLH'I'OI? Rudolph jzLBierwz'rth attorney Patented Aug. 3, 1943 DRYING METHOD Rudolph A. Bierwirth, Haddon Heights. N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application August 20, 1941, Serial No. 407,619

4 Claims.

This invention relates to drying method for expelling moisture from moisture-laden articles and has especial reference to the drying of waterladen rayon cakes.

In the manufacture of rayon, after the thread has been formed, it is wound upon a spool and thereafter placed in a cloth container, after which it is thoroughly washed in water to remove the sulphuric acid employed in coagulating the viscose material. The weight of the washed cakes, as they are known, is about three pounds, of which about two pounds is water and only one pound is rayon. To remove the water and dry the cakes, it has been customary to stack them in large drying rooms where heated air is circulated around them. Not only does this require a very large amount of space to take care of large-quantity production, butalso the drying time is from three to five days.

The primary object of my present invention is to provide a novel method of drying the rayon cakes or other similar articles which will not be subject to the aforementioned disadvantages.

More particularly, it is an object of my present invention to provide a novel method of drying the rayon cakes whereby the drying process is greatly accelerated, and hence the time required for drying greatly reduced.

Another object of my present invention is to provide an improved drying method as aforesaid by means of which the heat employed in the drying process will be applied uniformly to the articles to be dried."

It is also an object of my present invention to provide an improved drying method as aforesaid which involves a minimum number of steps and which can easily be carried out with great eflicacy even by one unskilled in the art.

In accordance with this invention, I provide a chamber capable of being evacuated and in which is placed the material to be dried. This material is placed between insulated electrodes which are connected to a source of radio frequency power. The radio frequency current flowing through the material heats it to the boiling point of the contained moisture. In the case of rayon or the like, the vacuum is of such a degree that the Water will boil off or evaporate at a temperature below that which will deleteriously affect the rayon. The water vapor may be condensed on the walls of the chamber by maintaining the walls of the chamber at a sufliciently low temperature, or a cooling coil may be provided in the chamber for condensing the liquid, after which it maybe pumped oil. In this way,

the water is removed from the material wii on raising the temperature above a fairly low temperature which is determined by the degree or vacuum maintained.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, as well as additional objects and advantages thereof, will best be understood from the following description, whenread in connection with the accompanying drawing, in which the single figure is a diagrammatic view of an arrangement employing the method of my invention.

Referring more particularly to the drawing, there is shown a container I providing a chamber which may be suitably evacuated by a vacuum pump or the like 3 connected to the chamber I through a condenser 5. Within the chamber l are a pair of spaced and preferably perforated electrodes 1 and 9 having external connection with a suitable source ll of radio frequency energy, such as an oscillator, through leads [2, l3, terminal posts I4, I 5, and leads I6, I l. The electrode 9 may be provided with a plurality of insulated legs I 8 which rest on the floor of the container l.

The material to be dried, such as the cake of rayon 20, is placed on the electrode 9, and the electrode 1 is placed on top of the cake 20 in parallel relation to the electrode 9, as clearly shown in the drawing. Thus, the cake 20 is disposed between but is in engagement with each of the electrodes 1 and 9, the electrodes extending beyond the cake. Rayon should not be heated above Fahrenheit, or the quality thereof will be impaired. Consequently, the vacuum pump 3 is operated to produce a vacuum of not less than 24 inches of mercury in the container l, since, at a vacuum of 24 inches of mercury or higher, the water may be driven off without raising the temperature above 140 Fahrenheit. Radio frequency voltage is then applied to the electrodes 1 and 9 from the oscillator I l to establish a uniform electrostatic field between the parallel electrodes, the dielectric losses in the article 20 between the electrodes 1 and 9 serving to heat the cake or other article and thereby evaporate or drive off the moisture therefrom. It will be noted, of course, that the heat is applied uniformly throughout the whole cake 20 by reason of the fact that the electrodes 1 and 9 are parallel to each other and extend beyond the cake 20, as clearly shown in the drawing, whereby all parts of the cake are concurter how much heat is applied to the cake.

, denserserves. to condense the p por hich'is removed from thecake 20. 'long'as' the vacuum within the container I is maintaining at24 inches of mercury or better and moisture is present in the rayon, the temperature cannot exceed 140 Fahrenheit no mat- The amount of heat generated in the cake or other article 20 is determined by the dielectric losses in the article and the voltage applied to the electrodes 1 and '9. The frequency at which the oscillator H is operated is a function of the voltage, the higher the voltage, the lower the frequency. Such' factors as a corona discharge between theelectrodes determine the maximum safe voltage to use, and once the voltage is determined, the "oscillator is operated at a frequency such as to deliver the required power. Theoscil- 'lator II should be capable of delivering from about 600 to "1000 watts per cake at a frequency of the order of 15 megacycles per second, although frequencies from about megacycles to 30 megacycles per second maybe found suitable. I have foundthat, by applying a moderate amount of power to the cake (about. 600 watts) the drying of the cake can be completely accomplished in about an hour, as compared with the three to five days required by the methods heretofore employed.

Although I have shown'a-nd described the application of my novel method to but a single cake of rayon, it is obvious that the same method may be employed in connection with a large number of such cakes, it being merely necessary to-make' the electrodes 1 and 9 large enough to accomtherefore, that my'invention shall not be limited except insofaras is; made necessary by the spirit of the appended claims.-

I claim as-my invention:

1. In the art of manufacturing rayon thread;

- the method of drying a moisture-laden rayon thread cake constituted bya thread wound on 'dtothe same, uniform electric itself in a plurality of rows which comprises subjecting the cake to a partial vacuum'such that water will evaporate therein at a temperature notexceeding 140 F., and, while said cake is under the influence of said vacuum, simultaneously subjecting all parts thereof to a high frequency electric field whereby all parts of said cake are heated as a result of the dielectirc losses therein to thereby'expel the moisture therefrom.

2.- In the art of manufacturing rayon thread, the method of drying a moisture-laden rayon thread cake constituted by a thread wound on itself in a plurality of rows which comprises subjecting the cake to a partial vacuum such that water will evaporate therein at a temperature not exceeding 140 F., and, while said cake is .under the influence of said vacuum, simultaneously subjecting all parts thereof to a uniform high frequency electric field whereby all parts of said cake are uniformly heated as a result of the dielectric losses therein to thereby expel the moisture'therefrom.

3. In the art of manufacturing rayon thread, the step of heating a water-laden rayon thread cake to expel the water therefrom, said cake being constituted by a thread wound on itself in a plurality of rows, which comprises subjecting all parts of the cake simultaneously to an oscillating electric field of the order of 15 megacycles per second While maintaining said cake in a partial I vacuum such that the water will evaporate therein at a temperature not exceeding F.

. 4. In the art of manufacturing rayon thread,

the method of drying a water-laden rayon thread cake constituted by a thread wound on itself in a plurality ofrows which comprises subjecting 

